Government Y had less than standard separation from air carrier X. System error.

Attributes
ACN	175974
Time
Date	199104
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : btv
State Reference	VT
Altitude	msl bound lower : 11000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zbw tower : mia
Operator	common carrier : air carrier
Make Model Name	Light Transport, High Wing, 2 Turboprop Eng
Flight Phase	cruise other
Route In Use	enroute : direct enroute airway : zbw
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	175474
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	none taken : insufficient time
Consequence	faa : investigated
Miss Distance	horizontal : 28200 vertical : 700
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

As the controller in charge, I was working air carrier X on a flight from bos to btv at 12000' MSL. I was also working government Y on a flight from btn to bos at 11000' MSL. The operational error occurred between btv and leb VOR's. When the aircraft were approximately 30 mi apart, nose to nose, I descended air carrier X to 6000' MSL. Upon further observation I decided to turn both aircraft 30 degrees left to ensure sep. I also activated the j-bar feature around air carrier X target to give me an idea of how much sep I had. (The j-bar feature is a 6 mi ring which circles an aircraft's target.) I asked air carrier X to report leaving 10000' MSL for traffic, but did not have the proper sep when the 2 aircraft passed. The aircraft were separated by 4.7 mi and 700'. This sep error could have been avoided by requesting that the descending aircraft increase the rate of descent or by leaving air carrier X at 12000' MSL until government Y passed and was at least 5 mi behind.

Original NASA ASRS Text

Title: GOV Y HAD LESS THAN STANDARD SEPARATION FROM ACR X. SYSTEM ERROR.

Narrative: AS THE CTLR IN CHARGE, I WAS WORKING ACR X ON A FLT FROM BOS TO BTV AT 12000' MSL. I WAS ALSO WORKING GOV Y ON A FLT FROM BTN TO BOS AT 11000' MSL. THE OPERROR OCCURRED BTWN BTV AND LEB VOR'S. WHEN THE ACFT WERE APPROX 30 MI APART, NOSE TO NOSE, I DSNDED ACR X TO 6000' MSL. UPON FURTHER OBSERVATION I DECIDED TO TURN BOTH ACFT 30 DEGS LEFT TO ENSURE SEP. I ALSO ACTIVATED THE J-BAR FEATURE AROUND ACR X TARGET TO GIVE ME AN IDEA OF HOW MUCH SEP I HAD. (THE J-BAR FEATURE IS A 6 MI RING WHICH CIRCLES AN ACFT'S TARGET.) I ASKED ACR X TO RPT LEAVING 10000' MSL FOR TFC, BUT DID NOT HAVE THE PROPER SEP WHEN THE 2 ACFT PASSED. THE ACFT WERE SEPARATED BY 4.7 MI AND 700'. THIS SEP ERROR COULD HAVE BEEN AVOIDED BY REQUESTING THAT THE DSNDING ACFT INCREASE THE RATE OF DSNT OR BY LEAVING ACR X AT 12000' MSL UNTIL GOV Y PASSED AND WAS AT LEAST 5 MI BEHIND.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.